Fermentation of an inoculated medium with Xanthomonas organisms for 36 to 72 hours under aerobic conditions results in the formation of xanthan gum, which is separated from other components of the medium by precipitation with acetone or methanol in a known manner. Because of the time required to ferment each batch, the low biopolymer content of the fermented medium and the processing steps including agitation required for production, recovery and purification of the product, xanthan is relatively expensive. Earlier work has indicated that the heteropolysaccharide produced by the action of Xanthomonas bacteria on carbohydrate media have potential application as film forming agents, as thickeners for body building agents in edible products, cosmetic preparations, pharmaceutical vehicles, oil field drilling fluids, fracturing liquids, and emulsifying, stabilizing and sizing agents. Heteropolysaccarides, particularly xanthan gum, have significant potential as mobility control agents in micellar polymer flooding. Xanthan gum has excellent viscosifying properties at low concentration. It is resistant to shear degradation, and exhibits only minimal losses in viscosity as a function of temperature, pH, and ionic strength. For these reasons, it is an attractive alternative to synthetic polyacrylamide for enhanced oil recovery operations.
However, in order for xanthan gum to be used in enhanced oil recovery operations as a mobility control agent, the cost must be sufficiently low to make such operations economical. It has been shown that the economics of xanthan fermentation are sensitive, at least in part, to the amount of energy necessary for mass transfer of oxygen, i.e., agitation of the fermenting medium. Mass transfer of oxygen to the growing cells is necessary, since approximately 1.5 grams of oxygen from the air is required to produce about 1 gram of cells and about 0.3 grams of oxygen is required to produce about 1 gram of xanthan gum.
Supply of the oxygen is accomplished through application of vigorous agitation to the viscous aerated fermentation broth. Experimental fermentations have demonstrated that more viscous systems require more agitation to maintain oxygen concentrations in the liquid above zero. Economic studies have shown that the cost of providing agitation amounts to between 10% and 30% of the total xanthan broth product cost. Any process improvements which enhance this mass transfer will improve the overall economics. Therefore, it would be advantageous to produce xanthan at normal concentrations in a fermentation, but with reduced viscosity, so as to lower mass transfer requirements. For example, in a normal fermentation process, reducing the viscosity of the xanthan gum broth from 4000 to 2000 cp can lower the per pound price of xanthan by as much as 10%.
Low viscosity xanthan is useful in certain fluid applications where a suspending agent is required, but where high viscosity is either not required or presents a disadvantage. To be a useful product for most applications, however, the viscosity of low viscosity Xanthan gum must be restored to that of a normal xanthan gum produced by typical fermentation.
Publications which are considered pertinent are as follows:
1. P. Rogovin, et al. 1970. "Continuous Fermentations Produce Xanthan Biopolymer: Laboratory Investigations". Biotechnology and Bioengineering, 12, p. 75-83.
2. M. C. Cadmus, et al, 1978, "Synthetic Media for Production of Quality Xanthan Gum in 20 Liter Fermenters". Biotechnology and Bioengineering, 20, 1003-1014.
3. Process for Production of Xanthan Gum, British patent application No. 2,008,138 A. Tate and Lyle.
In the pertinent publications, medium formulations call for sulfate ion as a growth nutrient, but sulfate ion as producing reduced viscosity xanthan is not noted.